PCB Anti-Interference Ability And Circuit Board Process Design

PCB's anti-interference ability

In order to make the designed products work better and effectively, the PCB design takes into account its anti-interference ability, the relationship with the specific circuit, and the reduction.

The importance of the design of the power line and ground line in the circuit board is to increase the size of the power line according to the size of the current flowing through the different circuit boards, so as to draw a conclusive conclusion. At the same time, the direction of the power line and the line and data retention constant. The anti-noise ability of electronic circuits. 

There are logic circuits and linear circuits on the PCB so that they should be separated as much as possible. The low-frequency circuit can be grounded in parallel at a single point. The actual wiring can be connected in series and then grounded in parallel. The high-frequency circuit is connected in series with multiple points. The ground wire should be short and thick. For high-frequency components, a large area of ground foil can be used. The ground wire should be as thick as possible. If the ground wire is very thin, the ground potential changes with the current, which will reduce the noise resistance. Therefore, the ground wire should be thickened so that it can reach the allowable current on the circuit board. If the design permits, the ground wire can be made with a diameter of more than 2-3mm. In digital circuits, the grounding wire is usually arranged in a loop to improve the noise resistance.

In PCB design, proper decoupling capacitors are generally placed on key parts of the printed circuit board. Connect a 10-100uF electrolytic capacitor across the line at the power input. Generally, a 0.01PF ceramic capacitor should be placed near the 20-30 pin, generally on the power pin of the 20-30 pin integrated circuit chip. A 0.01PF magnetic chip capacitor should be arranged nearby. For larger chips, there will be several power pins. It is best to add a decoupling capacitor near them. For chips with more than 200 pins, place them on the four sides. At least two decoupling capacitors are added. If the gap is insufficient, a 1-10PF tantalum capacitor can also be arranged with 4 to 8 chips. For components with weak anti-interference ability and large changes in power supply, the decoupling capacitor should be directly connected between the power line and the ground line of the component. , No matter what kind of lead wire connected to the capacitor is not easy to be too long.

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Circuit board process design

After the component and circuit design of the circuit board is completed, its process design should be considered when it is connected. The purpose is to eliminate various unfavorable factors before the start of production while taking into account the manufacturability of the circuit board in order to produce high-quality products and batches in production.
When talking about the positioning and wiring of the components, the process of the circuit board has been involved. The process design of the circuit board is mainly to organically assemble the circuit board and components we designed through the SMT production line, so as to achieve a good electrical connection and achieve the positioning layout of our designed product. Pad design, wiring, and anti-interference, etc. must also consider whether the board we designed is easy to produce, whether it can be assembled with modern assembly technology-SMT technology, and at the same time, it must be designed to prevent defective products during production height.

Specifically, there are the following aspects:

• 1.Different SMT production lines have their own different production conditions, but as far as the size of the PCB is concerned, the size of the PCB single board is not less than 200*150mm. If the long side is too small, imposition can be used, and the ratio of length to width is 3:2 or 4:3. When the size of the circuit board is larger than 200×150mm, the mechanical strength of the circuit board should be considered.
• 2. When the size of the circuit board is too small, it is difficult for the whole SMT production process, and it is not easy to mass-produce. The best way is to use the form of the jigsaw, which is to put 2, 4, 6, and other single boards according to the size of the single board. Combine them together to form a whole board suitable for mass production. The size of the whole board should be suitable for the size of the pasteable range.
• 3. In order to adapt to the mounting of the production line, the veneer should have a range of 3-5mm without placing any components, and the jigsaw should have a 3-8mm process edge. There are three types of connection between the process edge and the PCB: A without overlapping edges, There are separation grooves, B has overlapping edges and separation grooves, and C has overlapping edges but no separation grooves. It is equipped with blanking technology to build the country. According to the shape of the PCB board, etc. are suitable for different forms of the jigsaw. The positioning method of the PCB process side is different according to different models. Some need to be provided with positioning holes on the process side. The diameter of the hole is 4-5 cm. Relatively speaking, the positioning accuracy is higher than that of the side, so there is positioning. The hole-positioning model should be equipped with positioning holes when PCB processing and the hole design must be standard, so as not to cause inconvenience to production.
• 4.In order to better position and achieve higher placement accuracy, it is necessary to set a reference point for the PCB. Whether there is a reference point and whether the setting is good or bad directly affects the mass production of the SMT production line. The shape of the reference point can be square, round, triangle, etc. And the diameter should be within the range of 1-2mm, and the reference point should be within the range of 3-5mm, without any components and leads. At the same time, the reference point should be smooth and flat without any pollution. The design of the reference point should not be too close to the edge of the board, but a distance of 3-5mm.
• 5.From the overall production process, the shape of the board is preferably pitch-shaped, especially for wave soldering. The rectangular shape is convenient for transmission. If the PCB board has gaps, the gaps should be filled in the form of process edges. For a single SMT board, gaps are allowed. However, the gap should not be too large and should be less than 1/3 of the length of the side.

In short, the occurrence of defective products is possible in every link, but as for the design of the PCB board, we should consider all aspects so that it can not only achieve the purpose of our design of the product but also be suitable for the SMT production line in production. In mass production, try our best to design high-quality PCB boards to minimize the chance of defective products.